Dual-ended distributed temperature sensor with temperature sensor array

Abstract

Methods and apparatus are provided for distributed temperature sensing along an optical waveguide disposed axially with respect to a conduit using a distributed temperature sensor and an array of temperature sensors. An exemplary method includes performing distributed temperature sensing (DTS) using two ends of a first optical fiber disposed within the conduit and having a return path coupling the two ends, performing discrete temperature sensing based on measured reflections of light from reflective elements having characteristic wavelengths disposed at discrete locations, and determining temperatures at a plurality of locations based on the DTS and the discrete temperature sensing.

1 . An apparatus for determining temperatures associated with a conduit, comprising:
 an optical fiber having two legs coupled by a U-bend, a first end and a second end, wherein a first distance from the first end to the second end is smaller than a second distance from the first end to the U-bend.   
     
     
         2 . A system for determining temperatures associated with a conduit, comprising:
 a first optical fiber disposed within the conduit comprising two ends and having a return path coupling the two ends;   reflective elements having characteristic wavelengths disposed at discrete locations; and   at least one processor configured to:
 perform distributed temperature sensing (DTS) using the two ends of the first optical fiber, 
 perform discrete temperature sensing based on measured reflections of light from the reflective elements, and 
 determine temperatures at a plurality of locations based on the DTS and the discrete temperature sensing. 
   
     
     
         3 . The system of  claim 2 , wherein the at least one processor is further configured to calibrate the DTS based on the discrete temperature sensing. 
     
     
         4 . The system of  claim 2 , wherein the first optical fiber is disposed within coiled tubing. 
     
     
         5 . The system of  claim 2 , wherein the return path comprises a U-bend. 
     
     
         6 . The system of  claim 2 , further comprising:
 a second optical fiber, wherein the reflective elements are formed in at least the second optical fiber.   
     
     
         7 . The system of  claim 6 , wherein the at least one processor is further configured to determine a pressure at an end of the second optical fiber within the conduit. 
     
     
         8 . The system of  claim 7 , wherein the pressure is determined based on measured reflections from the second optical fiber. 
     
     
         9 . The system of  claim 2 , wherein:
 adjacent reflective elements have different characteristic wavelengths, and   the at least one processor is further configured to interrogate adjacent reflective elements using wavelength division multiplexing (WDM).   
     
     
         10 . The system of  claim 2 , wherein the reflective elements comprise fiber Bragg gratings (FBGs). 
     
     
         11 . The system of  claim 2 , wherein the first optical fiber comprises a continuous optical fiber with no splices between the first optical fiber and the reflective elements. 
     
     
         12 . A system for determining temperatures associated with a conduit, comprising:
 a first optical fiber disposed within the conduit comprising two ends and having a return path coupling the two ends;   reflective elements having characteristic wavelengths disposed at discrete locations; and   at least one processor configured to:
 perform distributed temperature sensing (DTS) using the two ends of the first optical fiber, 
 perform discrete optical power loss sensing based on measured reflections of light from the reflective elements, and 
 determine temperatures at a plurality of locations based on the DTS and the discrete optical power loss sensing. 
   
     
     
         13 . The system of  claim 12 , wherein the at least one processor is further configured to calibrate the DTS based on the discrete optical power loss sensing. 
     
     
         14 . The system of  claim 12 , wherein the first optical fiber is disposed within coiled tubing. 
     
     
         15 . The system of  claim 12 , wherein the return path comprises a U-bend. 
     
     
         16 . The system of  claim 12 , further comprising:
 a second optical fiber, wherein the reflective elements are formed in at least the second optical fiber.   
     
     
         17 . The system of  claim 16 , wherein the at least one processor is further configured to determine a pressure at an end of the second optical fiber within the conduit. 
     
     
         18 . The system of  claim 12 , wherein:
 adjacent reflective elements have different characteristic wavelengths, and   the at least one processor is further configured to interrogate adjacent reflective elements using wavelength division multiplexing (WDM).   
     
     
         19 . The system of  claim 12 , wherein the reflective elements comprise fiber Bragg gratings (FBGs). 
     
     
         20 . The system of  claim 12 , wherein the first optical fiber comprises a continuous optical fiber with no splices between the first optical fiber and the reflective elements.